WITHIN THE SCOPE OF A COOPERATIVE RESEARCH PROJECT AIMED AT THE DEVELOPMENT AND EVALUATION OF A NEW PROCESS FOR PRODUCING LIQUID HYDROCARBONS BY LOW TEMPERATURE AUTOCATALYTIC CONVERSION OF PHOTOSYNTHETIC MICROBIAL BIOMASS GROWN IN INTENSIVE OUTDOOR CULTURE AT THE INSTITUTE OF AGRICULTURAL MICROBIOLOGY OF THE UNIVERSITY OF FLORENCE, AN INVESTIGATION WAS CARRIED OUT FOR SELECTING PHOTOSYNTHETIC MICROBES GIVING A BIOMASS SUITABLE FOR CONVERSION INTO OIL. THE PARAMETERS THAT MAKE A PHOTOSYNTHETIC MICROBE A GOOD CANDIDATE FOR THIS PROCESS ARE THE YIELD OF PHOTOSYNTHETIC BIOMASS THAT CAN BE OBTAINED FROM OUTDOOR CULTURES AND THE EFFICIENCY OF ITS CONVERSION INTO OIL.
THREE ORGANISMS, REPRESENTATIVE OF VERY DIFFERENT MICROBIAL GROUPS, HAVE BEEN SELECTED FOR THESE EXPERIMENTS: RHODOPSEUDOMONAS PALUSTRIS, A PROKARYOTIC ANOXYGENIC PHOTO-ORGANOTROPH, SPIRULINA MAXIMA, A PROKARYOTIC FILAMENTOUS CYANOBACTERIUM AND PINNULARIA SP., AN EUKARYOTIC ALGA (DIATOM) ISOLATED FROM SEAWATER.

RHODOPSEUDOMONAS PALUSTRIS HAS BEEN GROWN IN A TUBULAR PHOTOBIOREACTOR MADE WITH TWO PLEXIGLAS PIPES CONNECTED BY TWO RECTANGULAR BOXES. THE CULTURE VOLUME WAS 120 LITRES AND THE ILLUMINATED SURFACE 1 SQ.METRE. THE PHOTOBIOREACTOR WAS IMMERSED IN A WATER BATH IN ORDER TO CONTROL EXCESSIVE HEATING DURING SUNNY DAYS. THE GROWTH MEDIUM WAS MADE WITH PARTIALLY DIGESTED PIGGERY WASTEWATER. THE CULTURE WAS RUN ON A SEMI-CONTINUOUS BASIS: EACH DAY A GIVEN AMOUNT OF CULTURE WAS WITHDROWN AND REPLACED WITH A EQUAL VOLUME OF WASTEWATER. THE BEST RETENTION TIME VARIED BETWEEN TWO AND FOUR DAYS ACCORDING TO THE ORGANIC MATTER CONTENT OF THE WASTE AND THE GROWTH RATE OF THE CULTURE.
THE BACTERIAL BIOMASS WAS HARVESTED BY FLOCCULATION WITH A CATIONIC POLYELECTROLYTE, FILTERED AND SUN DRIED. IN THE PERIOD APRIL-SEPTEMBER THE MEAN DAILY YIELD OF BIOMASS AMOUNTED TO 35 G (DRY WEIGHT) M TO THE POWER OF MINUS 2. IN JUNE AND JULY THE MEAN YIELD WAS CLOSE TO 40 G (DRY WEIGHT) M TO THE POWER OF MINUS 2. THE PERCENTAGE OD BOD REMOVAL RANGED FROM 80 TO 90%. THE RATIO BETWEEN THE AMOUNT OF BIOMASS PRODUCED VERSUS THE BOD REMOVED WAS 0.7. THE YIELD ON PIGGERY WASTEWATER WAS SOMEWHAT LOWER THAN ON SYNTHETIC MEDIUM, PRESUMABLY DUE TO THE YELLOWISH COLOUR OF THE WASTE THAT REDUCED THE AMOUNT OF LIGHT AVAILABLE TO THE BACTERIAL POPULATION.
SPIRULA MAXIMA WAS GROWN IN OPEN "RACEWAY" PONDS OF 25 SQ.METRES OF ILLUMINATED AREA. THE CULTURE MEDIUM WAS MADE WITH SUGAR-REFINERY WASTEWATER AFTER A PRELIMINARY PHOTOANAEROBIC RECLAMATION STAGE. THE BOD CONCENTRATION OF THE WASTEWATER WAS ABOUT 500. AN ADDITION OF 50 MQ OF SODIUM NITRATE PER LITER OF WASTEWATER WAS REQUIRED IN ORDER TO INCREASE THE AMOUNT OF ASSIMILABLE NITROGEN. THE BIOMASS WAS HARVESTED BY FILTRATION WITH A VIBROSCREEN. DURING THE PERIOD AUGUST-SEPTEMBER THE DAILY YIELD OF BIOMASS REACHED 18 G (DRY WEIGHT) M TO THE POWER OF MINUS 2.
PINNULARIA SP., A MARINE DIATOM, WAS GROWN IN A BATTERY OF 3,5 SQ.METRES "RACEWAY" PONDS. THE CULTURE MEDIUM WAS AN ARTIFICIAL SEAWATER PREPARED BY DISSOLVING 35 KG OF SEASALT IN ONE CUBIC METRE OF DEIONIZED WATER. THE ALGAL CELLS WERE HARVESTED BY GRAVITY SEDIMENTATION. THE SPENT CULTURE SOLUTION WAS RECYCLED INTO THE PONDS. DURING THE PERIOD MAY-SEPTEMBER THE MEAN DAILY YIELD AMOUNTED TO 16,5 G (DRY WEIGHT) M TO THE POWER OF MINUS 2. THE BIOMASSES OF THE THREE ORGANISMS SHOWED SOME DIFFERENCES IN COMPOSITION. THE SPIRULA BIOMASS HAS THE HIGHEST PROTEIN CONTENT AND THE LOWEST FAT CONTENT. THE BIOMASS OF PINNULARIA SP. IS RICH IN ASHES AND FATS. THE BIOMASS OF RHODOPSEUDOMONAS IS INTERMEDIATE BETWEEN THE TWO. PRODUCTION OF LIQUID HYDROCARBONS FROM THESE BIOMASSES IS UNDER INVESTIGATION AT THE INSTITUTE OF ORGANIC CHEMISTRY, UNIVERSITY OF TUEBINGEN. IF GOOD YIELDS OF LIQUID FUEL COULD BE ACHIEVED, AN EFFORD TO DEVELOP AND EVALUATE A PROCESS FOR LIQUID FUEL PRODUCTION USING PHOTOSYNTHETIC MICROBIAL BIOMASS AS SUBSTRATE WILL BE WORTH, PARTICULARLY WHEN THE PROCESS IS COUPLED TO THE RECLAMATION OF WASTEWATER.